1. Field of the Invention
This invention relates to an optical thin film, more particularly to an optical thin film including first and second light-condensing layers having different haze values. This invention also relates to an edge-type backlight module containing the optical thin film.
2. Description of the Related Art
A conventional display normally includes a screen and a backlight module configured to project light on the screen.
FIG. 1 illustrates an edge-type backlight module 1 for a flat panel display (not shown). The edge-type backlight module 1 includes a light source 11, a light guide plate (LGP) 12 which is disposed at one side of the light source 11, a reflector 13 which is disposed at a bottom of the LGP 12, a diffuser 15 which is disposed on the LGP 12, a first prism sheet 16 which is disposed on the diffuser 15, and a second prism sheet 17 which is disposed on the first prism sheet 16.
When light generated by the light source 11 passes through the LGP 12 and into the diffuser 15, it is scattered by the diffuser 15 before passing through the first prism sheet 16 and the second prism sheet 17. The first and second prism sheets 16, 17 subsequently collect and condense the scattered light from the diffuser 15.
However, the first and second prism sheets 16, can only collect incident light which has an incident angle in the range of −40° to −60° and 40° to 60°. As such, a portion of the scattered light (with the incident angle being outside of the range) cannot be collected and used for projecting onto the screen, which results in a decrease in the lighting efficiency of the backlight module.